Update Samples and Guides to use Lettuce

Favor lettuce because of multiplexing and improved scalability.
Using lettuce requires a fixed number of connections hence using
lettuce improves application scalability.

Fixes gh-652

samples/httpsession-redis-json/build.gradle

@@ -28,6 +28,7 @@ dependencies {
             "org.springframework.boot:spring-boot-starter-thymeleaf",
             "org.springframework.boot:spring-boot-starter-security",
             "nz.net.ultraq.thymeleaf:thymeleaf-layout-dialect",
+            "biz.paluch.redis:lettuce:$lettuceVersion",
             "org.apache.httpcomponents:httpclient"
 
     testCompile "org.springframework.boot:spring-boot-starter-test",

samples/httpsession-redis-json/src/main/java/sample/config/SessionConfig.java

@@ -19,7 +19,7 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 
 import org.springframework.beans.factory.BeanClassLoaderAware;
 import org.springframework.context.annotation.Bean;
-import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
+import org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory;
 import org.springframework.data.redis.serializer.GenericJackson2JsonRedisSerializer;
 import org.springframework.data.redis.serializer.RedisSerializer;
 import org.springframework.security.jackson2.SecurityJackson2Modules;
@@ -39,8 +39,8 @@ public class SessionConfig implements BeanClassLoaderAware {
 	}
 
 	@Bean
-	public JedisConnectionFactory connectionFactory() {
-		return new JedisConnectionFactory();
+	public LettuceConnectionFactory connectionFactory() {
+		return new LettuceConnectionFactory();
 	}
 
 	/**